METHOD AND APPARATUS FOR GENERATING TRAINING SEQUENCE CODES IN A COMMUNICATION SYSTEM
A method for generating a training sequence code (TSC) in a communication system. The method includes obtaining a full set of training sequence code candidates through joint channel estimation with consideration of a symbol delay of an interfering signal; optimizing cross-correlation properties for the full set; obtaining a subset for necessary training sequence codes among the training sequence code candidates; defining each of training sequence codes in the obtained subset as a reference sequence; and generating optimized training sequence codes by copying symbols of a predetermined number of bits located in the front of the reference sequence, arranging the copied symbols in Most Significant Positions (MSPs) as a guard sequence, copying symbols of a predetermined number of bits located in the rear of the reference sequence, and arranging the copied symbols in Least Significant Positions (LSPs) as a guard sequence.
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This application claims priority under 35 U.S.C. § 119(a) to a Korean Patent Application filed in the Korean Intellectual Property Office on Apr. 18, 2007 and assigned Serial No. 2007-38090, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates generally to a method and apparatus for generating training sequence codes in a communication system, and in particular, to a method and apparatus for generating training sequence codes in a Global System for Mobile Communication (GSM)/Enhanced Data Rates for GSM Evolution (EDGE) Evolution Radio Access Network (RAN) (hereinafter referred to as ‘GERAN’) system.
2. Description of the Related Art
Currently, the 3rd Generation Partnership Project (3GPP) Technical Specification Group (TSG)-GERAN standard conference is proceeding with GERAN Evolution for improving performance such as data transmission rate (or data rate) and spectral efficiency. As such, 16-ary Quadrature Amplitude Modulation (QAM) and 32-QAM, which are high-order QAM modulation schemes for improving downlink and uplink performances are added to Gaussian Minimum Shift Keying (GMSK) and Phase Shift Keying (8-PSK), which are the conventional modulation schemes.
Further, in order to increase data rate and spectral efficiency, for a symbol rate, a new rate of 325 Ksymbols/s is added to the existing rate of 270.833 Ksymbols/s. The new symbol rate, which is increased 1.2 times from the existing symbol rate, is applied to both the uplink and downlink, and will likely be reflected in the GERAN standard.
As described above, in the conventional GERAN system, the GMSK and 8-PSK modulation schemes are applied as modulation schemes. The GMSK scheme, a scheme for restricting a bandwidth by passing binary data through a Gaussian Low Pass Filter (LPF) and then performing frequency modulation thereon in a predetermined shift ratio, has excellent spectral concentration and high out-band spectral suppression as it enables a continuous change between two frequencies. The 8-PSK scheme, a scheme for modulating data so that it is mapped to a phase-shifted code of a carrier, can increase frequency efficiency. There are nine types of techniques for Packet Data Traffic CHannels (PDTCH) defined as a coding scheme used in the EDGE/EGPRS system. The nine types of techniques include nine types of Modulation and Coding Schemes (MCSs) MCS-1 to MCS-9 for EDGE/EGPRS. In actual communication, one of the various combinations of the modulation schemes and the coding techniques is selected and used. MCS-1 to MCS-4 use the GMSK modulation scheme and MCS-5 to MCS-9 use the 8-PSK modulation scheme. An MCS scheme used for transmission is determined according to the measured channel quality.
When the new rate of 325 Ksymbols/s is applied as described above, a new burst structure that is similar in form to that of
Further, in the synchronous networks, a symbol delay of an interferer burst is variable from −1 symbol to +4 symbols. Therefore, the influence of interfering TSC symbol delays on autocorrelation and cross-correlation properties should be considered during TSC design.
SUMMARY OF THE INVENTIONThe present invention has been designed to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a method and apparatus for generating TSCs of a symbol length 26 having cross-correlation properties based on the TSC structure used in the conventional GERAN system.
Another aspect of the present invention is to provide a method and apparatus for generating new TSCs of symbol lengths 30 and 31 to be applied to an improved data rate (325 Ksymbols/s) based on the TSC structure used in the conventional GERAN system.
In accordance with one aspect of the present invention, there is provided a method for generating a training sequence code (TSC) in a communication system. The method includes obtaining a full set of training sequence code candidates through joint channel estimation with consideration of a symbol delay of an interfering signal; optimizing cross-correlation properties for the full set; obtaining a subset for necessary training sequence codes among the training sequence code candidates; defining each of training sequence codes in the obtained subset as a reference sequence; and generating optimized training sequence codes by copying symbols of a predetermined number of bits located in the front of the reference sequence, arranging the copied symbols in Most Significant Positions (MSPs) as a guard sequence, copying symbols of a predetermined number of bits located in the rear of the reference sequence, and arranging the copied symbols in Least Significant Positions (LSPs) as a guard sequence.
The above and other aspects, features, and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness. Terms used herein are defined based on functions in the present invention and may vary according to users, operators' intention, or usual practices. Therefore, the definition of the terms should be made based on contents throughout the specification.
In designing TSCs to be applied to the GERAN system and GERAN system, the present invention considers all autocorrelation and cross-correlation properties and an influence of the properties on the interfering TSC delays, and uses a periodic TSC exhaustive computer search technique to search for an appropriate TSC. Further, in order to evaluate correlation properties among multiple sequences, Signal-to-Noise Ratio (SNR) degradation is introduced as a criterion. Moreover, in order to find binary TSCs having excellent cross-correlation properties, a Minimum-Average (Min-Ave) optimization method is introduced.
A description will first be made of a TSC arrangement structure according to an embodiment of the present invention.
Analyzing the GSM/EDGE standard document 3GPP TS 45.002, the conventional TSC arrangement structure of a symbol length 26 is illustrated in
x=(x1, x2, . . . , x26)=(a12, . . . , a16a1, . . . . a5, a6, . . . , a11, a12, . . . , a16, a1, . . . , a5) (1)
As shown in Equation (1), a TSC x is constructed in a periodic fashion by copying the last 5 symbols (or bits) A of the reference sequence (a1, a2, . . . , a16) composed of 16 symbols (or bits) and arranging them in the Most Significant Positions (MSPs) as a guard sequence, and by copying the first 5 symbols (or bits) of the reference sequence (a1, a2, . . . , a16) and arranging them to the Least Significant Positions (LSPs) as a guard sequence. The TSC x satisfies autocorrelation coefficients of Equation (2).
The autocorrelation coefficients of Equation (2) have the optimal autocorrelation properties for the range of non-zero shifts of an interested interval. Therefore, they have the properties that they are robust against interferer delays. In addition, up to six channel tap coefficients can be estimated with a simple correlator.
The present invention extends the conventional TSC structure of GSM/EDGE not only to
Before a description is given of a method for finding 8 sequences having symbol lengths 16 and 20, used for the reference sequences of the TSCs, Co-Channel Interference (CCI) for the symbol delay will be described.
In order to raise the spectral efficiency, as many carrier frequencies as possible should be reused. However, increasing carrier frequency reuse increases CCI in the networks. Therefore, to accurately estimate channel coefficients, it is preferable to use TSCs having both good autocorrelation and cross-correlation properties. However, the conventional TSCs used in GSM/EDGE are designed without considering their cross-correlation properties. When L-tap fading channels are considered, there is a possible symbol delay between a desired signal and an interfering signal in the synchronous network. In the common GSM network, a symbol delay (hereinafter denoted by ‘D’) of an interfering signal can be considered to be uniformly distributed within a range of [−1, 4] symbols. When D is considered, only the overlapped symbols between the desired TSC and interfering TSC can be used for joint channel estimation.
To evaluate the cross-correlation properties between multiple sequences, SNR degradation (hereinafter denoted by dSNR(dB)) can be used. dSNR is expressed as shown in Equation (3).
dSNR=10·log10(1+tr(φ−1)) (3)
In Equation (3), tr(φ−1) denotes a sum of main diagonal elements in matrix φ−1. As dSNR is lower, the cross-correlation properties of TSCs are superior.
Assuming that one interfering signal exists for each cell in the cellular communication system, mutual cross-correlation properties between TSCs should be optimized for joint channel estimation. If L(=5)-tap channel impulse responses of the carrier signal and the interfering signal are defined as hl=(hl,3, hl,2, . . . , hl,L+1), l=1, 2, the channel impulse responses for two co-channel signals can be defined as {tilde over (h)}=[h1 h2]. Two training sequences xl=(xl,1, . . . , xl,N), l=1, 2 are considered, and a TSC matrix is defined as {tilde over (X)}=[X1 X2] where the matrices Xl, l=1, 2, correspond to interferer delays for xl. The received signal y with consideration of CCI is y={tilde over (X)}{tilde over (h)}′+n, and as a result, the least square channel estimate can be calculated as shown in Equation (4).
ĥ=({tilde over (X)}′{tilde over (X)})−1{tilde over (X)}′y (4)
In Equation (4), X′ is the conjugate transpose of X. A correlation matrix necessary for calculating dSNR in Equation (3) is φ={tilde over (X)}′{tilde over (X)}.
Referring to
Similarly, when D<0, matrices X1 and X2 can be constructed based on
The present invention relates to new TSCs having two level signals. To maintain good autocorrelation properties against interferer delays of TSCs used in GSM/EDGE, new periodic TSCs proposed in the present invention adopt the TSC structure illustrated in
x=(x1, x2, . . . , xN)=(aN−2L−4, . . . , aN−2La1, . . . . a5, a6, . . . , aN−2L−5, aN−2L−4, . . . , aN−2L, a1, . . . , a5) (1)
Herein, a description will be provided for a method for searching for TSCs optimized with consideration of interferer delays according to an embodiment of the present invention. The embodiment of the present invention provides a method for generating 8 different TSCs having a 26-symbol length, 8 different TSCs having a 30-symbol length, and 8 different TSCs having a 31-symbol length, all of which can be used in the GERAN system. Although an exhaustive computer search method and a Min-Ave algorithm will be used in the description of the embodiment of the present invention, other methods can also be used herein as a method for obtaining a full set of TSC candidates and selecting 8 TSCs from them.
Step 1: Through an exhaustive computer search method, a full set of periodic TSCs candidates can be obtained, in which the autocorrelations of each sequence satisfy Equation (8).
In Equation (8), N denotes a symbol length of the TSC, and the reference sequence is (a1, a2, . . . , aN−2L). Reference sequences of even symbol lengths also satisfy Equation (7). For L=5, available sequence lengths include N=26 and N=30, and the total number of TSC candidates belonging to the full-set TSC of sequence lengths 26 and 30 is 512 and 5440, respectively. Since a change in sign for each symbol in a sequence will not affect the autocorrelation and cross-correlation properties, only a half of the TSC candidates belonging to the full-set TSC are used for optimization of cross-correlation properties of TSCs.
However, in step 208, if the autocorrelation Rs
Step 2: A TSC subset composed of a required number of TSCs is obtained by optimizing cross-correlations of the full-set TSCs. The optimization process uses the Min-Ave algorithm, which minimizes the TSC subset mean value of dSNR from the full set of TSCs.
Referring to
Find xj, j=1, . . . , U, where xj≠Y1, . . . , YS, that minimizes the mean dSNR in {xj,Y1}, . . . , {xj,Ys} and {Y1,xj}, . . . , {YS,xj} over all delays DdSNR (9)
However, if it is determined in step 306 that s>S−1, the Min-Ave algorithm performs Equation (10) in step 312, and increases u by 1 in step 314, and then returns to step 302.
Find the minimum within u
However, if it is determined in step 302 that u>U, the Min-Ave algorithm outputs the optimized binary sequences in step 316.
Step 3: Based on the reference sequences of 16 or 20-symbol length, found in Step 1 and Step 2, TSCs of 26 or 30-symbol length are constructed according to the TSC arrangement structure illustrated in
It is possible to construct TSCs of a 31-symbol length suitable for the high symbol rate of 325 Ksymbols/s according to the structures illustrated in
As is apparent from the foregoing description, the present invention provides TSCs with consideration of autocorrelation properties and cross-correlation properties. The use of the TSCs constructed with consideration of cross-correlation properties enables efficient data transmission/reception without performance reduction in the GERAN system. In addition, the TSCs proposed by the present invention can be applied on an extended basis even to 16-QAM and 32-QAM adopted by the GERAN system.
While the present invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.
Claims
1. A method for generating a training sequence code (TSC) in a communication system, the method comprising:
- obtaining a full set of training sequence code candidates through joint channel estimation with consideration of a symbol delay of an interfering signal;
- optimizing cross-correlation properties for the full set;
- obtaining a subset for necessary training sequence codes among the training sequence code candidates;
- defining each of training sequence codes in the obtained subset as a reference sequence; and
- generating optimized training sequence codes by copying symbols of a predetermined number of bits located in a front portion of the reference sequence, arranging the copied symbols in Most Significant Positions (MSPs) as a guard sequence, copying symbols of a predetermined number of bits located in a rear portion of the reference sequence, and arranging the copied symbols in Least Significant Positions (LSPs) as a guard sequence.
2. The method of claim 1, wherein obtaining the subset comprises:
- selecting necessary training sequence codes from the full set in an order of a training sequence code having a lower Signal-to-Noise Ratio (SNR) degradation.
3. The method of claim 1, wherein in generating the optimized training sequence codes, the reference sequence includes 16 bits, and each of the guard sequences arranged in the MSP and the LSP includes 5 bits.
4. The method of claim 1, wherein in generating the optimized training sequence codes, the reference sequence includes 20 bits, and the guard sequences arranged in the MSP and the LSP include 5 bits and 6 bits, respectively.
5. The method of claim 1, wherein in generating the optimized training sequence codes, the reference sequence includes 20 bits, and the guard sequences arranged in the MSP and the LSP include 6 bits and 5 bits, respectively.
6. The method of claim 1, wherein the training sequence code candidates satisfy: where L denotes a number of signal taps, and N denotes a number of bits of the training sequence code.
- x=(x1, x2,..., xN)=(aN−2L−4,..., aN−2La1,.... a5, a6,..., aN−2L−5, aN−2L−4,..., aN−2L, a1,..., a5) (1)
Type: Application
Filed: Apr 18, 2008
Publication Date: Oct 23, 2008
Applicant: SAMSUNG ELECTRONICS CO., LTD (Suwon-si)
Inventors: Yan XIN (Suwon-si), Jongsoon Choi (Suwon-si)
Application Number: 12/105,856
International Classification: H04L 27/28 (20060101);